In an optical network, signals can only travel along a given path so far before a regenerator is required. A regenerator converts a signal from an optical signal to an electronic signal, corrects any detected errors, and then converts the signal back to an optical signal with a better optical signal-to-noise ratio. A reachable path is one that does not require regeneration. A reach matrix describes all the nodes in the optical network that are connected by reachable paths. To connect all the nodes in the optical network, regenerators are placed between nodes for which there is no reachable path. It is advantageous to place regenerators at a limited number of sites since this placement allows regenerators to serve multiple possible traffic demands.
In today's optical networks, each wavelength is provisioned independently, and regenerators are placed where needed along the route with no systematic effort to consolidate regenerator sites. In addition, restoration capacity is pre-deployed, and therefore the regenerators deployed for restoration are dedicated to specific terminals. This limits the ability to share regenerators during various failure scenarios, and leads to the deployment of far more capital equipment. More recently, carriers have selected regenerator sites to minimize the number of regenerator sites required to guarantee that all traffic demands can be met. However, this site selection methodology neglects consideration of the required restoration capacity, in both site selection and in calculating the number of regenerators required for restoration.
With technology evolution and industry consolidation, a large carrier's dense wavelength division multiplexing (“DWDM”) optical network often includes several DWDM sub-networks from different vendors using different technologies. The DWDM sub-networks might vary in the number of wavelengths per fiber pair, data rate supported, and/or optical reachability parameters. These sub-networks may be part of a multi-layer network, wherein the IP traffic of a packet-layer is carried by the underlying optical layer. However, a customer requesting an end-to-end high-speed connection should not need to know the underlying heterogeneous sub-network infrastructure. It is the carrier's responsibility to optimize routing in its own heterogeneous network to save cost and to ensure high network availability. This requires a suite of network planning and circuit provisioning tools.
As new capabilities continue to be developed in optical communication networks, the planning tools used to build and provision these networks will become increasingly sophisticated. For example, reconfigurable-optical-add-drop multiplexers (“ROADMs”) were developed with the promise that far fewer regenerators would be needed in the network because wavelengths could express through ROADMs without regeneration. However, carriers immediately realized that efficient wavelength assignment algorithms were needed to avoid wavelength blocking. Without these algorithms, many regenerators would need to be deployed to act as wavelength converters, and the potential savings offered by ROADMs would not be fully realized. Recently, with the rise of software-defined networks (“SDNs”), and a more dynamically reconfigurable optical layer, the benefits of planning the optical layer and the packet layer of a multi-layer network in tandem have increased.